The invention relates to a continuous process for the production of cross-linked binding agent on the basis of unsaturated fatty acids and/or fatty acid esters, an elastic binding agent that can be produced by the process and the use of the elastic binding agent.
Binding agents made of natural oils today require relatively expensive preparation. For the production of the linoleum binding agent, today the following essentially distinct processes are known:
Bedford process (process presently used by all linoleum producers)
Taylor process (black oil)
Nettle process (hanging nettle paths are perfused with linseed oil)
Dripping process
Dxc3xcinneberg process (emulsion process)
Using these processes, the initial material for the binding agentxe2x80x94in the case of the production of linoleum natural oils, which contain various unsaturated fatty acids and/or fatty acid esters, are oxidized and cross-linked. The oxygen needed for the oxidation must be used in excess in all cases, so that only one part of the oxygen applied is used at any given for the reaction and ever-increasing quantities of air must be passed through the process, and thus large quantities of exhaust gas result. While the emissions are always decomposition products of vegetable fats, in other words, emissions of natural origin, they are still perceived as noxious smells. Therefore, nowadays, costly disposal units are required for the purification of the exhaust air, for example after-burn units.
Furthermore all the processes known in prior art are thoroughly inadequate, in that they also run only discontinuously (xe2x80x9cbatch processesxe2x80x9d) and require a long processing time for each charge. In addition to this, large units or several small units must always be acquired for these processes, in order to achieve low production costs for the binding agents.
The generally used Bedford process furthermore involves an unfavorable duration for each charge of up to 20 hours approximately, so that regardless of the number of orders a producing firm has, at least a three-shift operation is required.
Thus the object of the present invention is to provide a production process for binding agents, which should exhibit shorter processing times and a better use of oxygen, and also less exhaust air.
This object is attained by the embodiments designated in the claims.
In particular, a process for the production of a cross-linked binding agent on the basis of unsaturated fatty acids and/or fatty acid esters would be made available, which includes at least one foaming of a mixture containing unsaturated fatty acids and/or fatty acid esters with oxygen or with a gaseous mixture containing oxygen, and the reacting of the unsaturated fatty acids and/or fatty acid esters contained in the mixture through oxidation and cross-linking, in order to obtain the cross-linked binding agent.
The unsaturated fatty acids and/or fatty acid esters contained in the mixture to be reacted mainly originate from natural oils, particularly linseed oil. The reaction mixture containing unsaturated fatty acids and fatty acid esters is therefore also called xe2x80x9coilxe2x80x9d from now on. The concept of a gaseous mixture containing oxygen may also include pure oxygen.
Through the foaming of the gaseous mixture, the boundary surface or the contact surface between the oil and the oxygen is significantly increased. Because of this, a faster and more uniform interaction of the oxygen in the air with the surface of the oil takes place, so that more oxygen molecules per unit of time come into contact with unsaturated compounds of the unsaturated fatty acids and/or fatty acid esters.
The formation of foam, or the foaming, or the mechanical dispersion with the gaseous mixture containing oxygen in the mixture containing the unsaturated fatty acids and/or fatty acid esters can be carried out in three different ways:
1. The mixture is channeled through a system of steel pipes; the system integrates one or more static mixers one after another; these mixers create a finely dispersed and stable foam by feeding in a mixture of a gaseous mixture containing oxygen.
2. In place of the static mixers, dynamic mixers (rotor-stator principle), such as whipped foam mixers, can be used.
3. The vegetable oil can also be whipped in batches in a stirrer boiling vessel with dissolver and mixer disk, in such a way that a foam with fine cells results, which is fed into the overall continuous process.
As static mixers, the types SMV, SMF, SMXL, SMR and SMX of the Sulzer firm, or the Primixer type of the Striko firm, or the Primixer Quarto of the firm Fluitec CSE mixer are preferred. Especially preferred is the SMX type mixer of the Sulzer firm. As dynamic mixers, the types Eco Mix, Food Mix, Top Mix, Uni Mix or Compact Mix of the Hansa company are preferred for use, while the Top Mix or Uni Mix types of the Hansa firm are especially preferred. In static mixers, rotation speed of 2 to 100 l/min is preferred, preferably from 5 to 50 l/min.
The reaction speed of the oxidation and cross-linking of the unsaturated compounds in the mixture depends on the temperature of the mixture, or on the addition of reaction accelerators, or even on the quality of the foam. The quality of the foam includes both the fineness of the foam cells and the stability of the foam. The smaller the foam cells are, the greater the contract surface is between the gaseous mixture containing oxygen and the oil, and therefore the faster the oxidation of the unsaturated fatty acids and/or fatty acid esters takes place, and the faster the oxygen will be used up, and the more uniformly the mixture containing the fatty acids or the fatty acid esters will be oxidized and cross-linked. Thus, for a shorter reaction time, a fine-celled foam is preferred. Especially preferred is a foam weighing between 80 and 800 g per liter, and even more preferably between 150 and 500 g. To influence the structure of the foam and the stability of the foam, agents that increase surface interaction, such as lecithin or acetylated lecithin can be added to the mixture.
According to one embodiment of the process according to the invention, the viscosity of the mixture at the beginning of a reaction is generally still in the low range, for example between 50 and 80 mPas, so that the resulting foam is not yet very stable and will disintegrate if the pressure falls. However, this has the advantage that, because of the disintegration of the foam, a more effective exchange between the used air, i.e., air without oxygen or with a low oxygen content and new, unused air is attained. In terms of the technology of the process, it is thus preferable to run in so-called gassing cycles, in which the mixture is first intensively foamed with a gaseous mixture containing oxygen under a given pressure and then, after the reaction has taken place, it is again unfoamed through a drop in pressure, so that a new gassing cycle can be started up, in which the oil is preferably run in a circular process in a system made of steel pipe. In such a foaming process under pressure, the preliminary pressure of the oil can be set at 0.1 to 15 Mpa, more preferably between 0.1 and 5 Mpa, and most preferably between 0.2 to 2.0 Mpa, and the preliminary pressure of the gaseous mixture containing oxygen can be set between 0.15 and 5.5 Mpa, more preferably between 0.25 and 2.5 Mpa.
Furthermore there is preference for 1 to 1,000 cycles, with particular preference for 50 to 500 cycles for the foaming and reacting of the oil. As a result the treatment times for the cyclical foaming and reacting range from 5 min. to 8 hours, while the reaction at this stage of the process is preferably completed after 1 to 6 hours.
In another embodiment of the process according to the invention, the mixture defined above can be first foamed and then, using compression, be placed under pressure.
The speed of the reaction is also affected by the temperature of the reaction mixture. The temperature of the reaction during the reaction should preferably be between 10 and 150xc2x0 C., more preferably between 50 and 120xc2x0 C. Since the reaction is exothermic, the foam must be cooled as needed to control the reaction.